Installation

CocoaPods

Web3 is available through CocoaPods. To install it, simply add the following line to your Podfile:

pod 'Web3Swift.io'

Sending ethers

To send some wei from an account with a private key 0x1636e10756e62baabddd4364010444205f1216bdb1644ff8f776f6e2982aa9f5 to an account with an address 0x79d2c50Ba0cA4a2C6F8D65eBa1358bEfc1cFD403 on a mainnet:

import Web3Swift

let sender: PrivateKey = EthPrivateKey(
    hex: "0x1636e10756e62baabddd4364010444205f1216bdb1644ff8f776f6e2982aa9f5"
)

let recipient: BytesScalar = EthAddress(
    hex: "0x79d2c50Ba0cA4a2C6F8D65eBa1358bEfc1cFD403"
)

let network: Network = InfuraNetwork(
    chain: "mainnet",
    apiKey: "0c4d6dc730244b4185a6bde26f981bff"
)

let amount: BytesScalar = EthNumber(
    hex: "0xde0b6b3a7640000" // 10^18 in hex that represents 1 ETH
)

let response = try SendRawTransactionProcedure(
    network: network,
    transactionBytes: EthDirectTransactionBytes(
        network: network,
        senderKey: sender,
        recipientAddress: recipient,
        weiAmount: amount
    )
).call()

//If Ethereum network accepts the transaction, you could get transaction hash from the response. Otherwise, library will throw `DescribedError`
print(response["result"].string ?? "Something went wrong")

If you want to specify gas price or gas amount take a look at EthDirectTransactionBytes.swift.

To send ether instead of wei:

let ethAmount = 1.1

try SendRawTransactionProcedure(
    ...,
    weiAmount: EthToWei(
        amount: ethAmount
    )
).call()

Dealing with ERC-20 tokens

Sending tokens to an address

To send some ERC-20 tokens, for example OmiseGO, we need to get the smart contract address. OMG tokens are managed by smart contract at 0xd26114cd6EE289AccF82350c8d8487fedB8A0C07. In this example we send token from an account with a private key 0x1636e10756e62baabddd4364010444205f1216bdb1644ff8f776f6e2982aa9f5 to an account with an address 0x79d2c50Ba0cA4a2C6F8D65eBa1358bEfc1cFD403 on a mainnet:

import Web3Swift

let network: Network = InfuraNetwork(
    chain: "mainnet", apiKey: "0c4d6dc730244b4185a6bde26f981bff"
)

let sender: PrivateKey = EthPrivateKey(
    hex: "0x1636e10756e62baabddd4364010444205f1216bdb1644ff8f776f6e2982aa9f5"
)

let recipient: BytesScalar = EthAddress(
    hex: "0x79d2c50Ba0cA4a2C6F8D65eBa1358bEfc1cFD403"
)

let token: BytesScalar = EthAddress(
    hex: "0xd26114cd6EE289AccF82350c8d8487fedB8A0C07"
)

let amount: BytesScalar = EthNumber(
    hex: "0xde0b6b3a7640000" // 10^18 in hex that represents 1 OMG token
)

let response = try SendRawTransactionProcedure(
    network: network,
    transactionBytes: EthContractCallBytes(
        network: network,
        senderKey: sender,
        contractAddress: token,
        weiAmount: EthNumber(
            hex: "0x00" //We do not need to provide ethers to not payable functions.
        ),
        functionCall: EncodedABIFunction(
            signature: SimpleString(
                string: "transfer(address,uint256)"
            ),
            parameters: [
                ABIAddress(
                    address: recipient
                ),
                ABIUnsignedNumber(
                    origin: amount
                )
            ]
        )
    )
).call()

//If Ethereum network accepts the transaction, you could get transaction hash from the response. Otherwise, library will throw `DescribedError`
print(response["result"].string ?? "Something went wrong")

You can swiftly deal with other ERC-20 functions just by encoding another EncodedABIFunction .

Sending delegated tokens to an address

Here is an example of encoding transferFrom(from,to,value) function

EncodedABIFunction(
    signature: SimpleString(
        string: "transferFrom(address,address,uint256)"
    ),
    parameters: [
        ABIAddress(
            address: EthAddress(
                hex: "0xFBb1b73C4f0BDa4f67dcA266ce6Ef42f520fBB98"
            )
        ),
        ABIAddress(
            address: EthAddress(
                hex: "0x79d2c50Ba0cA4a2C6F8D65eBa1358bEfc1cFD403"
            )
        ),
        ABIUnsignedNumber(
            origin: EthNumber(
                hex: "0x01"
            )
        )
    ]
)

More encoding example including advanced ones are placed at Example/Tests/ABI

Checking an address balance

You do not need to send transaction for reading data from a smart contract. Here is an example of checking address balance by making a call to smart contract function balanceOf(owner).

let balance = try HexAsDecimalString(
    hex: EthContractCall(
        network: InfuraNetwork(
            chain: "mainnet", apiKey: "0c4d6dc730244b4185a6bde26f981bff"
        ),
        contractAddress: EthAddress(
            hex: "0xd26114cd6EE289AccF82350c8d8487fedB8A0C07" //OmiseGO token contract
        ),
        functionCall: EncodedABIFunction(
            signature: SimpleString(
                string: "balanceOf(address)"
            ),
            parameters: [
                ABIAddress(
                    address: EthAddress(
                        hex: "0xFBb1b73C4f0BDa4f67dcA266ce6Ef42f520fBB98" //Bittrex
                    )
                )
            ]
        )
    )
).value()

print(balance) // 13098857909137917398909558 is 13 098 857.909137917398909558 OMG tokens

Signing

import CryptoSwift

// Add your private key
let privateKey = EthPrivateKey(
        hex: "YOUR_PRIVATE_KEY"
)

// Form the bytes for your message
// In our example we sign null Ethereum address
let messageBytes = try! EthAddress(
        hex: "0x0000000000000000000000000000000000000000"
).value().bytes

// Create a message
// Don't forget that some services may expect
// a message with Ethereum prefix as here
let message = ConcatenatedBytes(
        bytes: [
            //Ethereum prefix
            UTF8StringBytes(
                    string: SimpleString(
                            string: "\u{19}Ethereum Signed Message:\n32"
                    )
            ),
            //message
            Keccak256Bytes(
                    origin: SimpleBytes(
                            bytes:
                    )
            )
        ]
)

// Use your custom hash function if needed
let hashFunction = SHA3(variant: .keccak256).calculate

// Create the signature
// Calculations are performed in a lazy way
// so you don't have to worry about performance
let signature = SECP256k1Signature(
        privateKey: privateKey,
        message: message,
        hashFunction: hashFunction
)

// Now you can retrieve all the parameters
// of the signature or use it for the signing with web3
let r = PrefixedHexString(
        bytes: try! signature.r()
)
let s = PrefixedHexString(
        bytes: try! signature.s()
)
let v = try! signature.recoverID().value() + 27

Getting information about transactions

Fetching information

Getting results of the recent or previous transaction is one of the most common tasks during developing interactions with DApps. There are two JSON-RPC methods for getting basic and additional transaction info. The first one is eth_getTransactionByHash (example) and the second one is eth_getTransactionReceipt(example). You could use next library example to get needed information from the Ethereum blockchain.

import Web3Swift
import SwiftyJSON

let transactionHash = BytesFromHexString(
    hex: "0x5798fbc45e3b63832abc4984b0f3574a13545f415dd672cd8540cd71f735db56"
)

let network = InfuraNetwork(
    chain: "mainnet",
    apiKey: "0c4d6dc730244b4185a6bde26f981bff"
)

let basicInfo: JSON = try TransactionProcedure(
    network: network,
    transactionHash: transactionHash
).call()

let advancedInfo: JSON = try TransactionReceiptProcedure(
    network: network,
    transactionHash: transactionHash
).call()

print(basicInfo["result"].dictionary ?? "Something went wrong")
/**
[
    "blockNumber": 0x196666,
    "value": 0x0,
    "v": 0x1b,
    "input":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,
    "hash": 0x5798fbc45e3b63832abc4984b0f3574a13545f415dd672cd8540cd71f735db56,
    "to": 0xbb9bc244d798123fde783fcc1c72d3bb8c189413,
    "transactionIndex": 0x7,
    "gasPrice": 0x4a817c800,
    "r": 0xd92d67e4a982c45c78c1260fc2f644ed78483e2bf7d6151aab9ea40a8e172472,
    "nonce": 0x0,
    "blockHash": 0x1f716531f40858da4d4b08269f571f9f22c7b8bd921764e8bdf9cb2e0508efa1,
    "from": 0xb656b2a9c3b2416437a811e07466ca712f5a5b5a,
    "s": 0x6ee7e259e4f13378cf167bb980659520a7e5897643a2642586f246c6de5367d6,
    "gas": 0x4c449
]
*/

print(advancedInfo["result"].dictionary ?? "Something went wrong")

/**
[
    "root": 0xee69c77c73cd53b90e928e786b1c7f5b743a36dccd877128cf1dce7b46980a97,
    "blockNumber": 0x196666,
    "transactionIndex": 0x7,
    "transactionHash": 0x5798fbc45e3b63832abc4984b0f3574a13545f415dd672cd8540cd71f735db56,
    "blockHash": 0x1f716531f40858da4d4b08269f571f9f22c7b8bd921764e8bdf9cb2e0508efa1,
    "from": 0xb656b2a9c3b2416437a811e07466ca712f5a5b5a,
    "contractAddress": null,
    "logsBloom": 0x00000000000000020000000000020000000000000000000000000000000000000000000000000000000000000000000000000000000000800000000000080000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000020000000000000000000200000000000000000000800000000000000000000000000000000000000000000000000001000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000000000000,
    "to": 0xbb9bc244d798123fde783fcc1c72d3bb8c189413,
    "logs": [
        {
            "blockNumber" : "0x196666",
            "topics" : [
                "0x5790de2c279e58269b93b12828f56fd5f2bc8ad15e61ce08572585c81a38756f",
                "0x000000000000000000000000000000000000000000000000000000000000003b"
            ],
            "data" : "0x000000000000000000000000b656b2a9c3b2416437a811e07466ca712f5a5b5a00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000001000000000000000000000000000000000000000000000000000000000000008000000000000000000000000000000000000000000000000000000000000000116c6f6e656c792c20736f206c6f6e656c79000000000000000000000000000000",
            "logIndex" : "0x5",
            "transactionHash" : "0x5798fbc45e3b63832abc4984b0f3574a13545f415dd672cd8540cd71f735db56",
            "removed" : false,
            "address" : "0xbb9bc244d798123fde783fcc1c72d3bb8c189413",
            "blockHash" : "0x1f716531f40858da4d4b08269f571f9f22c7b8bd921764e8bdf9cb2e0508efa1",
            "transactionIndex" : "0x7"
        }
    ],
    "gasUsed": 0x33da9,
    "cumulativeGasUsed": 0xf98e3
]
*/

NOTE: Library is still in development. Domain level objects for all RPC structures are on the roadmap.

Parsing transaction

After fetching the information you could transparently convert it to suitable objects.

// Get the number of the block in which the transaction occurred
let block = try HexAsDecimalString(
    hex: EthNumber(
        hex: basicInfo["result"]["blockNumber"].stringValue
    )   
).value()

print(block)
// 1664614

// Get the recipient of the transaction
let recipient = try EthAddress(
    hex: basicInfo["result"]["to"].stringValue
).value().toHexString()

print(recipient)
// bb9bc244d798123fde783fcc1c72d3bb8c189413

// Get the transaction fee in WEI
let gasPrice = EthNumber(
    hex: basicInfo["result"]["gasPrice"].stringValue
)

let gasUsed = EthNumber(
    hex: advancedInfo["result"]["gasUsed"].stringValue
)

let fee = try HexAsDecimalString(
    hex: gasPrice * gasUsed
).value()

print(fee)
// 4247860000000000 WEI = 0,00424786 ETH

Parsing transaction's input data

You could easily parse any transaction's input by knowing it's ABI or types the data passed into it.

// Parse the transaction input parameters
/*
    newProposal(
        [0] address _recipient,
        [1] uint256 _amount,
        [2] string _description,
        [3] bytes _transactionData,
        [4] uint256 _debatingPeriod,
        [5] bool _newCurator
    )
*/

// Prepare the transaction's input for parsing - trim the signature of the executed function
let input = ABIMessage(
    message: TrimmedPrefixString(
        string: SimpleString{
            basicInfo["result"]["input"].stringValue
        },
        prefix: SimpleString{
            "0x612e45a3"
        }
    )
)

// Get the recipient's address
let abiRecipient = try DecodedABIAddress(
    abiMessage: input,
    index: 0
).value().toHexString()

print(abiRecipient)
// b656b2a9c3b2416437a811e07466ca712f5a5b5a

// Get the description string
let description = try DecodedABIString(
    abiMessage: input,
    index: 2
).value()

print(description)
// lonely, so lonely

// Get the debating period number
let debatingPeriod = try HexAsDecimalString(
    hex: DecodedABINumber(
        abiMessage: input,
        index: 4
    )
).value()

print(debatingPeriod)
// 604800

// Get the boolean flag
let flag = try DecodedABIBoolean(
    abiMessage: input,
    index: 5
).value()

print(flag)
// true

Author

• Timofey Solonin @biboran, abdulowork@gmail.com
• Vadim Koleoshkin @rockfridrich, vadim@zerion.io

License

Web3Swift is available under the Apache License 2.0. See the LICENSE file for more info.